316 A MANUAL OF AMERICAN LAND SHELLS. 



ture diagonal, subregiilarly lunate; peristome witli a heavy white 

 thickening, uniforuily subanguhirly reflected, its coluuiellar portion 

 subdilated. Greater diameter 18^, lesser 16""" ; height, 11^"»°>. 



EiVix dausa, Say, Journ. Pliila. Acad., ii, 154 (1821); American Couch. (1832), No. 4, 

 pi. xxxvii, lig. 1 ; Bixxey's ed., 17, pi. xxxvii, fig. 1 ; ed. Chenu, Bibl. Couch., 

 iii, 50, pi. xiii, fig. 2. — Bixney, Bost. Journ. Nat. Hist., i, 482, pi. xv (1837); 

 Terr. Moll., ii, 107 (excl. syn.), pi. iv (excepting the outline figures). — De 

 Kay, N. Y. Moll., 31, pi. iii, fig. 13 (1843).— Eeeve, Con. Icon., fig. 694.— 

 Bland, Ann. N. Y. Lye, vi, 336.— Pfeiffer, Mon. Hel. Viv., iv, 321.— W. G. 

 BiNXEY, Terr. Moll., iv, 46; L. & Fr.-W. Sh., i, 149 (1869). 



Helix rennsijlvanica, Pfeiffer, ex parte, Synib. ad. Hist. Hel., ii, 36 ; Mon. Hel. Viv., 

 i, 291 ; in Chemnitz, ed. 2, ii, 51, ex parte. — Eeeve, ex parte, Con. Icon., 

 No. 676 ; not of Green. 



Helix MitchelUana, Pfeiffer, in Chemnitz, 1. c, i, 332, pi. Ivi, figs. 6-8. 



Mesodon dausa, Tky-qn, Am. Journ. Conch., iii, 47 (1867).— W. G. Binney, Terr. 

 Moll., V, 332. 



A Post-Pliocene species, now found in the Interior Region, in the 

 States bordering on the Ohio Eiver and in Wisconsin, Missouri, Ten- 

 nessee, Mississii)pi, and Alabama. 



Animal blaclcish. 



In .1/. clansus the umbilical region is more widely excavated, and the 

 groove behind the reflected peristome, ])roducing the contraction of the 

 aperture, is continued at the base of the shell, becoming wider as it 

 joins the umbilical opening. In M. Mitchellianus the groove is almost 

 obliterated, at the point of reflection of the peristome over the umbili- 

 cus, by the more tumid character of the last whorl. 



Helix Ingalhiana, Shuttleworth {JugaUsiana, err. typ., of Albers, ed. 



Pjg 39 2), is a small form of daiisi(s. I give a figure copied from 

 an unpublished plate of Shuttleworth. It has since been 

 published in Fischer's Notitire, II, Plate III, Fig. 5, 

 Jaw as usual in the genus ; about 10 stout ribs. 



H. IvqalUiana. 



(Sbmtiewoitii.) Lingual membrane as in M. thyroides (Terr. Moll., V, 

 Plate VII, Fig. T) ; it has 41-1-41 teeth, with about 11 perfect laterals. 

 I can detect no side cusps, even on the extreme outer marginals. 



The genitalia are figured in Terr. Moll., V, Plate XIY, Fig. G. The 

 penis sac is the conspicuous feature of the system ; it is longer than 

 the oviduct and almost as stout, of about equal size throughout ; it 

 has the entrance of the vas deferens and retractor muscle at its blunt 

 apex. The genital bladder is small, lengthened oval, with a long, slen- 

 der duct. The prostate is narrow, stout, prominent, cord-like. The 

 vas deferens is large. The other organs present no peculiar features. 



